Theoretical astrophysics and plasma physics at RPC

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AGN as potential factories for eccentric black hole mergers

Nature Springer Nature 603:7900 (2022) 237-240

Authors:

J Samsing, I Bartos, Dj D'Orazio, Z Haiman, B Kocsis, Nwc Leigh, B Liu, Me Pessah, H Tagawa

Abstract:

There is some weak evidence that the black hole merger named GW190521 had a non-zero eccentricity1,2. In addition, the masses of the component black holes exceeded the limit predicted by stellar evolution3. The large masses can be explained by successive mergers4,5, which may be efficient in gas disks surrounding active galactic nuclei, but it is difficult to maintain an eccentric orbit all the way to the merger, as basic physics would argue for circularization6. Here we show that active galactic nuclei disk environments can lead to an excess of eccentric mergers, if the interactions between single and binary black holes are frequent5 and occur with mutual inclinations of less than a few degrees. We further illustrate that this eccentric population has a different distribution of the inclination between the spin vectors of the black holes and their orbital angular momentum at merger7, referred to as the spin–orbit tilt, compared with the remaining circular mergers.

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Three-Dimensional Inhomogeneity of Electron-Temperature-Gradient Turbulence in the Edge of Tokamak Plasmas

(2022)

Authors:

JF Parisi, FI Parra, CM Roach, MR Hardman, AA Schekochihin, IG Abel, N Aiba, J Ball, M Barnes, B Chapman-Oplopoiou, D Dickinson, W Dorland, C Giroud, DR Hatch, JC Hillesheim, J Ruiz Ruiz, S Saarelma, D St-Onge
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Secular Spin-orbit Resonances of Black Hole Binaries in AGN Disks

(2022)

Authors:

Gongjie Li, Hareesh Gautham Bhaskar, Bence Kocsis, Douglas NC Lin
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Black Hole Discs and Spheres in Galactic Nuclei -- Exploring the Landscape of Vector Resonant Relaxation Equilibria

(2022)

Authors:

Gergely Máthé, Ákos Szölgyén, Bence Kocsis
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Relativistic non-thermal particle acceleration in two-dimensional collisionless magnetic reconnection

Journal of Plasma Physics Cambridge University Press (CUP) 88:1 (2022) 905880114

Abstract:

Magnetic reconnection, especially in the relativistic regime, provides an efficient mechanism for accelerating relativistic particles and thus offers an attractive physical explanation for non-thermal high-energy emission from various astrophysical sources. I present a simple analytical model that elucidates key physical processes responsible for reconnection-driven relativistic non-thermal particle acceleration in the large-system, plasmoid-dominated regime in two dimensions. The model aims to explain the numerically observed dependencies of the power-law index $p$ and high-energy cutoff $\gamma _c$ of the resulting non-thermal particle energy spectrum $f(\gamma )$ on the ambient plasma magnetization $\sigma$ , and (for $\gamma _c$ ) on the system size $L$ . In this self-similar model, energetic particles are continuously accelerated by the out-of-plane reconnection electric field $E_{\rm rec}$ until they become magnetized by the reconnected magnetic field and eventually trapped in plasmoids large enough to confine them. The model also includes diffusive Fermi acceleration by particle bouncing off rapidly moving plasmoids. I argue that the balance between electric acceleration and magnetization controls the power-law index, while trapping in plasmoids governs the cutoff, thus tying the particle energy spectrum to the plasmoid distribution.
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